The primary objective of the proposed research is to investigate the ability of the 1981 and 1991 NIOSH equations to predict and control low-back injuries. This will be achieved through a 3-year prospective field investigation using subjects from a variety of occupations. Selecting subjects from a variety of occupations will allow the results to be applied to a variety of individuals and industries. The prospective study will include several industries and 200 subjects working in the industries selected for inclusion in the study. Comprehensive job data will be collected in the form of work place geometry, task durations, etc. Personal data on the subjects will also be collected such as age, gender, ethnicity, history of lost time low- back injuries, etc. The evaluation of the NIOSH equations will be performed along two basic dimensions. The first dimension is an investigation of the relationship between the ratios of the magnitudes of loads lifted or lowered to the 1981 Action Limit and 1991 Recommended Wight Limit and the probability of injury. NIOSH has defined these ratios as the Lifting Index and has suggested that the LI be used as a job design parameter to assess injury potential and to design and redesign tasks and jobs. The relationship between LI and injury probability is not known and the proposed research will quantify this relationship. the secondary evaluation of the first phase will be an investigation of whether personal variable s such as age, gender, etc., modify the relationship between the LI and injury probability. As well as incidence of injury the severity of injuries in terms of days lost per injury will also be investigated. The second phase of the evaluation will focus on the form of the multiplier included in the 1981 and 1991 NIOSH equations. These multipliers (asymmetry, coupling, distance, frequency, horizontal location, and vertical location) have specific functional forms determined, primarily, with biomechanical, physiological and psychophysical considerations. The proposed research will investigate the relationship between each of these variables and the probability of injury. The benefit of this analysis is that the epidemiological evidence can be used to either confirm or suggest modifications to the current forms of the individual multipliers. The proposed research will serve to advance the knowledge of job and task design principles aimed at reducing the incidence and severity of low- back injuries in industry. The results will benefit workers involved in manual materials handling, by reducing the potential for injuries, and will also benefit employers who experience economic burdens associated with injuries. The proposed research will also provide NIOSH with valuable information concerning the adequacy of the current lifting guidelines as well as provide information that may be useful in future revisions of the lifting guidelines.